The business correspondence doesn't stop once the contract is signed; you may have several additional occasions to discuss the matter through letters. For example, if you have a contract with a university as a tenure-track professor, then you will receive several additional pieces of correspondence that refer to your contract, such as when your benefits begin and many other matters that you must address when you begin work. As a supervisor, you may often have to write letters that cite the original contract in a way that will remind the employee or client where he can find the information.
Tell the recipient what she needs to know, then draw her attention to the contract or the area in the contract that contains the essential information. For example, "Your benefits will begin two weeks after your start date, as stated on line 5a on page 2 of your contract." You do not need a formal citation style such as American Psychological Association (APA) style to cite the contract; just refer to the relevant contract and page number.
Consider if you need to quote sections of the contract instead of merely referring to it. If the contract is long or very complex, you should quote the relevant section and then explain on which page number and section number the information is located.
Tell the recipient that you would be glad to provide another copy of the contract for his reference if he has lost his copy. Give him your contact information, such as your e-mail address or telephone number if he has questions or would like to request an additional copy of the contract.